Tire testing systems and methods

ABSTRACT

Systems and methods, including: one of a simulated road surface and an actual road surface; a test tire physically contacting the one of the simulated road surface and the actual road surface; and a plurality of gears linking the test tire and the one of the simulated road surface and the actual road surface, such that the velocities of the test tire and the one of the simulated road surface and the actual road surface are linked and an associated slip ratio between the test tire and the one of the simulated road surface and the actual road surface is controlled. The simulated road surface includes one of a drum, a belt, a drive wheel, and a rail. The plurality of gears are varied in terms of gear ratio using a controller such that slip ratio is dynamically controlled and varied.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present patent application/patent is a continuation-in-part (CIP) ofco-pending U.S. patent application Ser. No. 13/087,872, filed on Apr.15, 2011, and entitled “TIRE TESTING SYSTEMS AND METHODS,” which claimsthe benefit of priority of U.S. Provisional Patent Application No.61/324,935, filed on Apr. 16, 2010, and entitled “RAILED TIRE TESTINGFACILITY,” U.S. Provisional Patent Application No. 61/346,068, filed onMay 19, 2010, and entitled “CARROUSEL TIRE TESTING FACILITY,” and U.S.Provisional Patent Application No. 61/414,625, filed on Nov. 17, 2010,and entitled “CARRIAGE AND OTHER ENHANCEMENTS FOR TIRE TESTING,” thecontents of all of which are incorporated in full by reference herein.The present patent application/patent also claims the benefit ofpriority of U.S. Provisional Patent Application No. 61/533,960, filed onSep. 13, 2011, and entitled “TIRE TESTING SYSTEMS AND METHODS” and U.S.Provisional Patent Application No. 61/587,178, filed on Jan. 17, 2012,and entitled “RAILED TIRE TESTING FACILITY,” the contents of both ofwhich are incorporated in full by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to tire testing systems andmethods for evaluating the performance of tires, and thereby enhancingthe performance of vehicles and the like. The present invention alsorelates generally to vehicle simulation.

BACKGROUND OF THE INVENTION

Tire performance is easily one of the most significant parametersdictating vehicle performance, and has therefore resulted in extensivetire testing needs at both tire and automotive development andmanufacturing facilities. Tire testing equipment has progressedsignificantly, evolving from single-drum machines and twin-roller testsets to flat-track machines with higher load and slip angle capacities.

However, in recent years, three developments in tire testing needs have,for the most part, gone unaddressed. The first is the fact that, duringthe past decade, there have been a number of events which have causedfederal regulators (Congress and the U.S. National Highway TrafficSafety Administration, or NHTSA), public interest groups, the military,and the media to focus on consumer safety related to tires, vehiclehandling, and rollover. This concern for safety has resulted in revisedand updated federal motor vehicle safety standards for tires (the TREADAct, for example) and regulations related to dynamic rollover testingfor vehicles.

A second significant need has surfaced with recent advances that havebeen made in electronic stability control (ESC). Testing of ESC systemshas indicated that single vehicle crashes may be reduced by 34% forpassenger cars, and 59% for sport utility vehicles, resulting in 5,300and 9,600 lives saved annually, respectively. In response to this data,NHTSA issued a new regulatory rule in April of 2007 entitled FMVSS-126;Electronic Stability Control Systems, that will require all vehiclesunder 10,000 lbs to be equipped with ESC systems. The NHTSA regulationrequires the performance of a prescribed “sine and dwell steeringmaneuver test” to determine the vehicle's ability to prevent loss ofcontrol and rollover events. The regulation was phased in beginning in2009, when 55% of the vehicles manufactured were to comply with theregulation, and it reached full compliance on Sep. 1, 2011. The militaryis also heavily involved in conducting tests to prevent rollover events,a significant cause of injuries and fatalities during deployment.

In order to meet the FMVSS-126 criteria, vehicle manufacturers have theoption of building multiple prototype vehicles for testing, a veryexpensive process, or investing in simulation capabilities which enablefaster design convergence and time to market, reduced labor costs, andreduced prototyping costs. However, a key component to simulation isaccurate tire data. Current tire testing machines are extremely limitedin slip angles and steer rates, as well as dynamic loading capabilities,and are therefore inadequate for simulating the maneuvers required byFMVSS-126.

A third demand driver is provided by the racing industry, where highspeeds, horsepower, and hard braking into a corner provide extreme loadsto the tire. None of the current tire testing facilities have theability to generate longitudinal (driving or braking) loads ofsufficient magnitude and speeds to emulate racing conditions. This hasbecome more and more important, particularly in racing venues likeNASCAR and Formula One, to ensure the safety of the driver andperformance of the tire under various racing conditions. The stakes arefurther elevated by the fact that some races generate $100 million tothe local economy, and delays or cancelations caused by failure of acomponent are often televised nationally and internationally.

Along with these three principal drivers, various OEM's havehistorically expressed interests in other testing capabilities as wellincluding modeling various terrains and surfaces (for example, wetroads, ice, and sand/mud applications) and hardware in the loop (HIL)capabilities (for more accurately simulating braking systems, etc.).These are not currently available on conventional testing machines.

BRIEF SUMMARY OF THE INVENTION

In one exemplary embodiment, the present invention provides a tiretesting system, including: a first rail and a second rail; a carriageassembly coupled to the first rail and the second rail such that fivedegrees of freedom of motion of the carriage assembly are therebyconstrained; a first bogie assembly coupling the carriage assembly tothe first rail such that at least lateral, pitch, and yaw motions of thecarriage assembly are thereby constrained; and a second bogie assemblycoupling the carriage assembly to the second rail such that at leastvertical and roll motions of the carriage assembly are therebyconstrained; wherein the carriage assembly translates in a directionthat is tangential to the first rail. This configuration makes the tiretesting system advantageously insensitive to the parallelism of the tworails, their thermal expansion, etc. The tire testing system alsoincludes a tire articulation system coupled to the carriage assembly,wherein the tire articulation system includes a dedicated actuator foreach degree of freedom of motion of a test tire coupled thereto. Thisassembly represents the constraints of a typical vehicle. Each of thededicated actuators includes at least one of a force-based actuator anda displacement-based actuator. Optionally, the tire articulation systemfurther includes a lateral motion mechanism that is actuated by adisplacement-based actuator, a vertical elevator that is actuated by aforce-based actuator, a torque mechanism that is actuated by aforce-based actuator, a camber mechanism that is actuated by adisplacement-based actuator, and a steering mechanism that is actuatedby a displacement-based actuator, although there may be applicationsrequiring different actuator types for any of the degrees of freedom.Optionally, the tire articulation system includes an arcuate camberbearing that has a fixed radius, such that it rotates exactly on centerfor only a single sized tire. Test tires of different sizes areaccommodated by the camber bearing by compensation with lateral motion,which serves to eliminate any “scrub.” Optionally, the carriage assemblyis translated with respect to the first rail and the second rail byrotation of a test tire coupled to the carriage assembly with respect toa road surface. Optionally, the carriage assembly is translated withrespect to the first rail and the second rail by rotation of a drivetire coupled to the carriage assembly with respect to a road surface.Optionally, the carriage assembly is translated with respect to thefirst rail and the second rail by rotation of a pair of drive tirescoupled to the carriage assembly with respect to a fin structuredisposed on a road surface. Optionally, the carriage assembly istranslated with respect to the first rail and the second rail by a drivemechanism coupled to the carriage assembly and one or more or the firstrail and the second rail. Optionally, the carriage assembly istranslated with respect to the first rail and the second rail by a cablesystem coupled to the carriage assembly. Optionally, the first rail andthe second rail each include a plurality of rigidly connected (e.g.welded) segments that prevent disturbances in the system caused byexpansion joints, for example. Optionally, the first rail and the secondrail each define a slight bow, which also helps to preserve railalignment while allowing for deflection, thermal expansion, etc.Optionally, the carriage assembly further includes a cutting or dressingapparatus for removing imperfections in the first rail, the second rail,and/or a road surface, along with appropriate kinematic andsurface-averaging systems. Optionally, the carriage assembly furtherincludes paver and/or roller for maintaining constant distance from thefirst and/or second rails as a road surface is paved. Preferably, thetire testing apparatus further includes one or more of a road surface, abelt, and a drum disposed adjacent to the first rail and the secondrail, optionally covered with a material similar to that used on aconventional tite testing machine (for example, 3M-ite, Polycut, or asimilar abrasive material). This allows for the calibration of roadsurface data with belt data, for example. Optionally, the carriageassembly includes a drive wheel and a test wheel having a predeterminedgear ratio between them, providing a slip ratio carriage.Advantageously, the tire testing system of the present invention followsthe SAE convention for motion by default, and does not require softwarecorrection that could lead to parasitic errors. Of course, any of thecomponents of the tire testing system may also be driven or braked, asappropriate.

In another exemplary embodiment, the present invention provides a tiretesting method, including: providing a first rail and a second rail;providing a carriage assembly coupled to the first rail and the secondrail such that five degrees of freedom of motion of the carriageassembly are thereby constrained; providing a first bogie assemblycoupling the carriage assembly to the first rail such that at leastlateral, pitch, and yaw motions of the carriage assembly are therebyconstrained; providing a second bogie assembly coupling the carriageassembly to the second rail such that at least vertical and roll motionsof the carriage assembly are thereby constrained; wherein the carriageassembly translates in a direction that is tangential to the first rail;and providing a tire articulation system coupled to the carriageassembly, wherein the tire articulation system includes a dedicatedactuator for each degree of freedom of motion of a test tire coupledthereto.

In a further exemplary embodiment, the present invention provides a tiretesting method, including: providing a first rail and a second rail;providing a road surface disposed adjacent to the first rail and thesecond rail; providing a carriage assembly coupled to the first rail andthe second rail such that five degrees of freedom of motion of thecarriage assembly are thereby constrained; providing a first bogieassembly coupling the carriage assembly to the first rail such that atleast lateral, pitch, and yaw motions of the carriage assembly arethereby constrained; providing a second bogie assembly coupling thecarriage assembly to the second rail such that at least vertical androll motions of the carriage assembly are thereby constrained; whereinthe carriage assembly translates in a direction that is tangential tothe first rail; and providing a tire articulation system coupled to thecarriage assembly, wherein the tire articulation system includes adedicated actuator for each degree of freedom of motion of a test tirecoupled thereto. Optionally, the method also includes providing one ormore of a belt and a drum disposed adjacent to the first rail and thesecond rail, optionally covered with a material similar to that used ona conventional tite testing machine (for example, 3M-ite, Polycut, or asimilar abrasive material). Optionally, the carriage assembly includes adrive wheel and a test wheel having a predetermined gear ratio betweenthem.

In a still further exemplary embodiment, the present invention providesa tire testing system, including: one of a simulated road surface and anactual road surface; a test tire physically contacting the one of thesimulated road surface and the actual road surface; and a plurality ofgears linking the test tire and the one of the simulated road surfaceand the actual road surface, such that the velocities of the test tireand the one of the simulated road surface and the actual road surfaceare linked and an associated slip ratio between the test tire and theone of the simulated road surface and the actual road surface iscontrolled. Optionally, the simulated road surface includes one of adrum, a belt, a drive wheel, and a rail. The plurality of gears arevaried in terms of gear ratio using a controller such that slip ratio isdynamically controlled and varied. Optionally, the plurality of gearsinclude a continuously variable transmission. Optionally, the pluralityof gears include a worm gear, a ring gear, and a plurality of bevelgears.

In a still further exemplary embodiment, the present invention providesa tire testing system, including: a first rail and a second rail,wherein one or more of the first rail and the second rail includeseparate substantially horizontal and substantially vertical plates; acarriage assembly coupled to the first rail and the second rail suchthat five degrees of freedom of motion of the carriage assembly arethereby constrained; a first bogie assembly coupling the carriageassembly to the first rail such that at least lateral, pitch, and yawmotions of the carriage assembly are thereby constrained; and a secondbogie assembly coupling the carriage assembly to the second rail suchthat at least vertical and roll motions of the carriage assembly arethereby constrained; wherein the carriage assembly translates in adirection that is tangential to the first rail.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings, in which like reference numbers are used todenote like system components/method steps, as appropriate, and inwhich:

FIG. 1 is a perspective view of one exemplary embodiment of the tiretesting system of the present invention;

FIG. 2 is another perspective view of one exemplary embodiment of thetire testing system of the present invention;

FIG. 3 is a perspective view of another exemplary embodiment of the tiretesting system of the present invention;

FIG. 4 is a perspective view of a further exemplary embodiment of thetire testing system of the present invention;

FIG. 5 is a perspective view of a still further exemplary embodiment ofthe tire testing system of the present invention;

FIG. 6 is a perspective view of a still further exemplary embodiment ofthe tire testing system of the present invention;

FIG. 7 is a perspective view of a still further exemplary embodiment ofthe tire testing system of the present invention;

FIG. 8 is a perspective view of a still further exemplary embodiment ofthe tire testing system of the present invention;

FIG. 9 is a schematic diagram illustrating one exemplary embodiment of atrack configuration associated with the tire testing systems of thepresent invention;

FIG. 10 is a perspective view of one exemplary embodiment of a tirewarm-up station that may be used in conjunction with the tire testingsystems of the present invention;

FIG. 11 is a schematic diagram illustrating the system constraintsrequired to emulate vehicular constraints on a tire;

FIG. 12 is a top planar view of one exemplary embodiment of a carriageof the tire testing systems of the present invention;

FIG. 13 is a perspective view of one exemplary embodiment of a carriageof the tire testing systems of the present invention;

FIG. 14 is another perspective view of one exemplary embodiment of acarriage of the tire testing systems of the present invention;

FIG. 15 is a schematic diagram illustrating one exemplary embodiment ofa system for deterministically setting the slip ratio regardless ofvelocity of the present invention;

FIG. 16 is a front planar view of one exemplary embodiment of a drivesystem for the carriage of the tire testing systems of the presentinvention;

FIG. 17 is a series of side planar views of one exemplary embodiment ofa high-speed cable drive system for the carriage of the tire testingsystems of the present invention;

FIG. 18 is a schematic diagram illustrating one exemplary embodiment ofthe dynamic slip ratio control system and method of the presentinvention, which utilizes displacement inputs, rather than torqueinputs;

FIG. 19 is another schematic diagram illustrating one exemplaryembodiment of the dynamic slip ratio control system and method of thepresent invention, which utilizes displacement inputs, rather thantorque inputs;

FIG. 20 is a schematic diagram illustrating one exemplary embodiment ofa rail structure used in conjunction with the tire testing systems andmethods of the present invention;

FIG. 21 is a schematic diagram illustrating another exemplary embodimentof a rail structure used in conjunction with the tire testing systemsand methods of the present invention;

FIG. 22 is another schematic diagram illustrating another exemplaryembodiment of a rail structure used in conjunction with the tire testingsystems and methods of the present invention;

FIG. 23 is a further schematic diagram illustrating another exemplaryembodiment of a rail structure used in conjunction with the tire testingsystems and methods of the present invention; and

FIG. 24 is a still further schematic diagram illustrating anotherexemplary embodiment of a rail structure used in conjunction with thetire testing systems and methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The objective of the tire testing facility of the present invention isto provide the finest tire testing capabilities in the world for thepassenger car, light truck, racing, and defense industries, amongothers. Specifically, this objective is met through the successfulcompletion of the following sub-objectives:

-   -   Specifying, designing, and building a force and moment tire        testing machine to address the specific needs of FMVSS-126 by        providing required loads and sweep rates to emulate the sine and        dwell test and other maneuvers required by the protocol;    -   Developing testing capabilities that allow high input torque        (˜10,000 Nm) and braking capabilities (˜7,000 Nm) for the        acquisition of longitudinal data under typical driving and        racing conditions;    -   Providing a platform that meets the needs of the racing industry        through high speed (˜200 mph) testing and representative loads        and slip angles;    -   Providing a multi-use machine that meets or exceeds testing        capabilities of current tire testing facilities in range and        accuracy;    -   Providing a means for collecting tire data under various        environmental conditions, including rain, snow, and variations        in temperature;    -   Providing a means for determining the effects of ambient        conditions on the resulting grip capacity of a tire running on a        paved surface;    -   Providing a means for measuring tire data for heavy duty tires;    -   Providing the capability to conduct durability studies using        cleats and other features in a paved surface;    -   Providing a method for comparing data from belt machines to data        taken from a tire on a real road surface;    -   Providing a means for simulating a vehicle emergency maneuver        and gathering tire force and moment data;    -   Providing a means for verifying tire models by collecting data        under the modeled loads and displacements; and    -   Developing “Hardware in the Loop” capabilities for tire testing,        where a simulation controls inputs to the machine in real time,        allowing the machine to collect data in real time and feed it        back to the simulation, which in turn responds with new load and        displacement commands for the machine. This capability could        lead to the elimination of many test vehicles prior to        production.

This represents a new approach to tire testing. Current testinginstrumentation typically consists of one of several configurations: a)a single-drum roller test, b) a double-drum roller test, c) abelt-driven system, or d) a trailer-based dynamometer. The single anddouble-drum roller tests fail to replicate a real roadway condition,because the test tire rolls on the outside or inside diameter of theroller, thereby providing an undesirable concave or convex contact patchon the tire. In addition, the surface that the tire runs on does notresemble that of asphalt or concrete, which most roads are made of. Thebelt-driven systems provide a flat contact surface, but utilize either astainless steel or 80-120 grit sandpaper surface to replicate the roadsurface. They also suffer from speed constraints and limits to lateralloads and steer rates. Trailer-based dynamometers are limited in loadcapacity, suffer from compliance and variation in the trailer, and arelimited in speed.

Thus, the present invention provides a new generation of testinginstrumentation which provides realistic data representing the forcesand moments provided by the tire on asphalt pavement, cement pavement,or other terrains.

Referring to FIGS. 1 and 2, in the design of the present invention, theroad surface 12 is stationary and is paved using the same materials andmethods as the road surface being emulated. The metrology head 14translates along a railed system 16 which provides stiffness, accuracy,and repeatability to the system 10. As the tire 18 translates down theroadway 12, forces and moments are measured to assess the performance ofthe tire 18.

The principal advantage of this system 10 is the ability to engineer theroad surface 12 to more closely emulate a real road. The tradeoff isfound in the necessity to transfer power and data to and from themetrology head 14, as well as the potential for a considerably largermachine footprint. A significantly larger footprint makes it moredifficult to control the environment, which can affect repeatability.

This system 10 is based, in part, on technologies developed by theroller coaster industry. This tracked design opens a new set ofpossibilities for tire testing, as well as suspension testing. The mostobvious advantage is that of the road surface 12. In a tracked system,the roadway 12 can be paved using a conventional asphalt compound, avariety of asphalt compounds (to emulate variations across the country),and/or concrete surfaces. Interestingly, the inclusion of a rail switch(not illustrated) to change to different circuits of the track may allowsections where the track can be soaked to study wet traction, wet andfrozen to emulate icy conditions, or replaced with sections for mud,sand, or other terrains.

Modularity is a significant advantage to the system 10 of the presentinvention. Once the track 12 and rail 16 are laid, bogies 20 (the cartscarrying the metrology head 18) can be specifically designed to addressparticular needs. For example, measuring rolling resistance requiresvery sensitive measurement, but measuring braking performance requires amuch stiffer system which negates sensitivity. In this design, you canhave one carriage 20 for sensitive, low friction applications and asecond carriage 20 for high load conditions. Some of the configurationsand capabilities are listed in the following paragraphs:

-   -   Standard configuration as shown in FIG. 1, where the tire 18        rolls without a powered driving torque, but with applied steer        angles and normal loads;    -   A high sensitivity, low load condition suitable for measuring        rolling resistance;    -   A “soft” system with little noise suitable for measuring road        noise;    -   Driven configuration, where the tire 18 can be driven using a        hydraulic or electric motor or similar means;    -   The configuration shown in FIG. 3, where the rail 16 is        sub-surface to facilitate easy resurfacing of the road surface        12 as well as to minimize the moment created by the tire 18;    -   A configuration such as that shown in FIG. 4, where a suspension        system 22 is incorporated to examine the effects of coupling the        tire 18 to the suspension 22. This capability may enable vehicle        engineers to test new suspension concepts, as well as to tune        the suspensions 22 for different maneuvers. Tunable components        may be investigated, such as the JRi Controlled Damper, where        damper characteristics can be actively changed while on the        track. This system 10 allows very quick studies in optimizing        suspension performance, so that the final production damper can        be later designed to match the optimized characteristics of the        controlled damper. This leads to significantly shorter times to        production and reduced prototyping costs.    -   With the tracked system 10, numerous carriages 20 can operate        simultaneously, as shown in FIG. 5, thereby opening the        possibility of not only improving throughput at the facility,        but also being able to emulate all four tires 18 on a vehicle        simultaneously. For example, the addition of        Hardware-in-the-Loop (HIL) capabilities in the baseline        specifications for the machine 10 is possible. HIL systems        combine actual components and systems with computer simulations        to overcome the difficulties of modeling nonlinearities,        hysteresis, and other hard-to-predict losses. In the case of a        tire/suspension subsystem, the machine 10 can take steering        input from a simulation, apply it on the test rig to measure        resulting forces and moments (which are highly nonlinear), feed        that back to the simulation in real time to predict vehicle        response, and feed the simulated response back into the        mechanical testing system 10 to alter the applied input, such as        vertical deflection. Rather than generating tire data at        discrete camber angles and slip angles, the system generates the        “exact” condition in real time. This capability revolutionizes        the development process for vehicles, since a full suspension        can be tested prior to building a prototype vehicle. In        addition, since multiple bogies 20 can operate on the track 12        simultaneously, all four corners of the vehicle can be        simulated, resulting in more accurate predictions of the        understeer gradient, rollover events, and overall traction.

The only prior disadvantage of the tracked system 10 was primarily incontrolling the environment, as well as monitoring the changingcharacteristics of the asphalt surface 12 as it cures and goes throughheating cycles which cause the oils to rise to the surface. Accordingly,the track 12 may be covered/protected, either with a metal building,overhang, precast concrete structure, cloth structure, or inflatablestructure. Obviously, this adds significantly to the cost of thefacility, particularly if air conditioning is required. However, it maybe feasible to cover a small circuit, say for passenger car testing, ora longer circuit used for racing applications.

Referring to FIG. 6, in an alternative exemplary embodiment, the tiretesting facility 30 of the present invention involves a test tire 18running on the inner diameter of a large circular roadway 12 supportedby a carrousel structure 32. Note that FIG. 6 is conceptual only, andmany details (including some of the reaction tires 34) are not included.The large forces exerted by the tire 18 on the road surface 12 areopposed primarily by reaction tires 34 running directly opposite thetest tire 18 on the outer diameter of the road 12, as well asperpendicular to the test tire 18 on the edges of the roadway 12. Thetire loading mechanism includes and reacts against the support tires 34,not directly against the roadway 12. This minimizes stresses within thecarrousel structure 32. Moderate, coincidental forces are able to bereacted by the carousel itself 32. The carrousel 32 has a largediameter, roughly 60 feet, in order to minimize the curvature of theroadway surface 12 contacting the tire 18. The road support structure isa box cross-section ring, providing stiffness in all modes. Obviously,the only intended degree of freedom for the road/ring is pure rotationin the horizontal plane, about the center of the ring. The carrousel'smotion is further controlled and stabilized by stationary high speedtires 34, along the periphery of the ring, in both axial and radialorientation. The road surface 12 is cast using a ceramic such asaluminum oxide to closely emulate various road surfaces while providingmaterial stability and repeatability. Although not asphalt, thismaterial can be designed to closely emulate asphalt while also beingcleanable. The circular track rotates past the tire station 36. Thisdesign facilitates the inclusion of environmental controls, as it couldeasily fit within a 20,000 square foot facility. Multiple tire stations36 can be utilized, and tire/suspension systems are also possible.

The key advantages of this system include:

-   -   More realistic road surface 12 than sandpaper used on many drum        and belt machines;    -   Flatter contact patch than smaller drum machines;    -   High speeds, enabled by size of the structure that minimizes        stresses;    -   Ability to control environment as opposed to an outdoor        facility;    -   Ability to utilize multiple measurement stations; and    -   Ability to utilize multiple road surfaces 12 to emulate        variations in asphalt across the country or other road surfaces,        such as concrete.

Thus, in various exemplary embodiments, the present invention provides atire testing system 10 (FIGS. 1-5) that utilizes the best features ofcurrent tire testing facilities while eliminating or reducing thenegative features of such facilities. The resulting system 10 is onewhere the road surface 12 (FIGS. 1-5) is a paved, stationary, asphalt orconcrete surface that removes the uncertainty of emulating a roadsurface since it is paved using similar techniques and materials. Thearticulated spindle assembly and the associated metrology (measurement)instrumentation 14 are supported on a carriage 20 which translates downa guide rail 16, as illustrated in FIGS. 1-6. The system 10 is composedof two very proven subsystems.

Referring to FIGS. 7 and 8, in another alternative exemplary embodiment,the spindle assembly 42 is similar to that commonly found ontrailer-based systems but modified to allow high rates of motion toemulate the “sine with dwell” and similar tests. The carriage and railsystem 40 is similar to those found in the roller coaster industry. Theconcept is similar to the NASA Advanced Landing Dynamics Facility (ALDF)located at Langley Air Force Base in that it involves a carriage whichsupports a test tire and instrumented spindle assembly and translatesdown a rail.

The tire testing system 40 of the present invention may be used for thequantification and correction of tire testing grip paper degradationthrough a comparison with on-road data. Most lab-based tire testingsystems use either drums or belts to replicate a road surface. Thesedrums and belts are typically covered with 80 or 120 grit sandpaper orequivalent to allow the tire to grip the surface and generate similarforce data to the data that come from an on-road test. Published dataillustrate that the sand paper loses grip and “gives up” generating tireforces long before the tire on the road does, meaning that the sandpapercovered test surfaces quickly lose integrity depending on load, slipratio, and even the manufacturer (different manufacturers use differentbinders and abrasives).

The present invention provides an on-road system 40 that can also beparked over a belt simulated road system to provide side-by-sidecomparisons of the grip data generated by the tire 18. This system 40eliminates the need to change tires 18 to different measuringinstruments, which would increase expense and reduce accuracies.Optionally, the “road” system surface may be covered with a materialsimilar to that used on a conventional tite testing machine (forexample, 3M-ite, Polycut, or a similar abrasive material)

The present invention also allows for the study of the effects of curveradii on tire performance and road features such as cleats and rumblestrips. The track configuration provides several pertinent features. Inone exemplary configuration, the overall structure resembles a teardropshape, providing two long straightaways 51 and 52 connected by twocorners 53 and 54, one of large radius 53 and the other with a tighterradius 54. This type of track 50 is shown in FIG. 9. The straightaways51 and 52 allow for 5-8 seconds of data acquisition depending on speed,ensuring uninterrupted data flow without changes in travel trajectory.These sections 51 and 52 also allow for comparison with typical flatbelt tire testing instruments, which are unable to simulate road radiusin cornering situations (i.e., in real cornering, the inner part of thecontact patch covers less distance than the outer due to road curvature,an effect not replicated on a belt system). The two curves 53 and 54provide realistic cornering conditions, where the velocity vectorsbetween the inner part and outer part of the contact patch differ.Although an infinite selection of radii is not possible, inclusion oftwo curves of differing radii 53 and 54 allows the industry's first lookat the effects curvatures have on tire grip. In addition, progressivebanking can be included in the two curves 53 and 54 to study the effectbanking has on grip as well. A large number of curves with varying radiican also be included; for example, many race tracks refer to “turn 1,turn 2, turn 3, turn 4, and so on indicating that multiple radii canexist in a nominally oval track.

The inclusion of a rail switch to change to different circuits of thetrack 50 allows sections where the track 50 can be soaked to study wettraction, wet and frozen to emulate icy conditions, or replaced withsections for mud, sand, rocky or other terrains. It is also easy toincorporate features such as squiggle, cleats, and rumble strips in thepaved surface 12.

Referring to FIG. 10, in a further alternative exemplary embodiment, thetire testing facility of the present invention allows for the directcalibration of a tire 18 running on a stationary drum, belt, or othertesting machine 62 with a tire 18 running on real asphalt. A flat beltsystem 60 is incorporated in the track circuit as a “warm-up station,”allowing for the calibration of road-based data directly with flat-beltdata.

Given the changes in environmental conditions on the outdoor track,ensuring repeatability is given highest priority. The solution issimple. Prior to entering the circuit, the carriage 20 is positioned inan environmentally-controlled room over a flat belt roller 62 and lockedin place, effectively turning the system 60 into a standard flat-belttesting system. The tire 18 and belt 62 accelerate to speed, warm up,and run through a prescribed testing cycle while acquiring data usingthe instrumented spindle 64. Once the warm-up cycle is completed, theshuttle 20 exits the room and enters the track, where it repeats thesame cycle on real pavement. Note that the same measurementsystem/spindle 64 is used for both indoor and track based testing,reducing or eliminating errors from using two different systems.

This procedure not only ensures repeatability for the tests, butprovides a means for baselining each tire 18 in the controlledenvironment prior to testing on the track. Tire performance can then beassessed under a variety of ambient conditions representative of thosethat will exist on the highway, thereby providing the vehicle designerwith a performance envelope from which best and worst case scenarios canbe replicated. In addition, a witness tire program can be implementedwhich will allow assessment of changes to pavement/tire gripcharacteristics as ambient conditions and the road surface change.

In general, the tire testing systems 10, 40, and 60 of the presentinvention provide an optimally-constrained instrumented test spindle. Inorder to minimize system uncertainty, the carriage 20 is used to applythe same kinds of constraints to the tire 18 that the vehicle wouldnormally provide. This is shown in FIG. 11. A vehicle provides loadingto the tire through the spindle, with the independent parameters beingthe longitudinal force, Fx, (representing the inertia of the vehicle),lateral force, Fy, (representing the lateral inertia of the vehicle),normal force, Fz, (representing gravitational forces), applied torque,Ty, (representing driving and braking torques), slip angle, α, andcamber, γ. Since the lateral force is determined by slip angle ratherthan steer angle or vehicle heading, it is appropriate to substitutelateral force with lateral displacement, y, as a constraint. Obviously,the applied forces are opposed in the contact patch.

The carriage and rail system 10, 40, and 60 is ideal for replicatingthese constraints on the tire 18. Actuation can be simplified andoptimized to match the load or displacement constraints; for example,hydraulic or pneumatic actuators can be used to apply the normal(gravitational) loading, while ball or lead-screw actuators are optimalfor displacement actuation. With this philosophy, the load inputs areprovided through linear induction motors or traction drives on thecarriage 20 for Fx, pneumatic or hydraulic actuators for Fz, and anelectric drive for torque. The rail 16 provides constraint of thelateral displacement, while screw type actuators drive the camber andslip angles. Using this approach, the vehicle can be fully replicated.

Referring to FIGS. 12-14, the first challenge is to ensure that thecarriage 70 which translates down the rail 16 is minimally butsufficiently constrained, so that the only designed degree of freedom isthe longitudinal motion in the x-direction. This is achieved throughvery careful design, since using two rails such as are common in theroller coaster industry would be subject to motion errors if the railswere not exactly parallel and equidistant at all times. There are twosets of bogies (rollers) 72 on the main rail 17, and one set 74 on theopposing rail 19. The two sets 72 on the main rail 17 are sufficient toconstrain lateral motion, vertical motion, pitch motion, and yaw motionfor the carriage 70, regardless of the relative position of the oppositerail 19. The bogie 74 on the opposing side constrains only the verticalmotion, therefore completing the restraint of roll and verticaldisplacement. This system is robust against thermal expansion, reducesthe importance of alignment of one rail to the other, and enablesoptimal preloading to reduce compliance in the system.

The carriage components including the longitudinal translation stage(carriage 20 translating on rail 16), vertical stage 76 (provides normalloading through hydraulic actuator), lateral translation stage, rotaryturn table 78 (for steer), and camber pivot 80. The rotary and camberdegrees of freedom are actuated through displacement actuators.

The present invention also provides a method for positively controllingslip ratio with minimal energy input via a positive contact device thatcontrols the relative slip between two objects (for example, a tire anda road surface) through a gear train such that slip is restricted to theregion between those two objects. The gear train is used to alter therelative displacement (angular, translational, or other) or velocity ofone object over the other in a fixed, known ratio. The gear train can beused to replace independent force or torque-based drives for the twoobjects, thereby eliminating unwanted dynamics due to lack of stiffnessand robustness in those drives.

Tire testing machines today typically control velocities of the road (ortrailer) while also controlling the rotational velocity of the tire, andthen measure the resulting slip ratio (rather than controlling itdirectly). Unfortunately, system dynamics make it very difficult tocontrol the two velocities relatively and accurately. In addition, usingthe tire testing carriage as an example, two motors are needed for thisscenario, one to drive the carriage, and the other to drive the testwheel. Each motor must generate significant power to overcome the speedrequirements, since Power=Torque×ω. Even small torques can require largepower if the speeds are high.

To explain the difficulty, consider the following example. First,realize that the slip ratio is a function of the difference in thevelocity of the carriage and the tangential velocity of the tire, or,the difference in the displacement of the carriage and the tangentialdisplacement of the tire over a given increment in time. This is theparameter that you are trying to control, with two, independent force(or torque) inputs.

This is analogous to trying to move a table with rubber feet an exactdistance. Say you wish to move that table 1.1 mm to the right. If youpush on the table, it will resist movement until the friction gives way,and you will likely grossly overshoot the target 1.1 mm. On the otherhand, if you attached a screw device to a rigid frame of reference andthen screwed the table over, you would be much more likely to hit yourtarget. In the first scenario, you are trying to hit a displacementtarget with force inputs. In the second, you will be much moresuccessful because you have provided a stiff, controlled displacementinput. This is the approach the present design takes.

The present invention provides a method for deterministically settingthe slip ratio regardless of velocity. The method is best explained bythe very simple representation shown in FIG. 15. In FIG. 15, assume thatthe gear 80 and the test tire 18 have the same diameters. Also assumethat they act under pure rotation, and the gearbox (a continuouslyvariable transmission, or CVT, or a planetary gear set) 82 translates ata specified velocity. The CVT 82 can provide gear ratios greater or lessthan one, but rather than doing so in discrete increments, it can do soin infinitesimally small increments. If the gear ratio of the CVT 82 isvaried to 1.1:1 rather than 1:1, then the test tire will rotate slowerthan the gear, resulting in a braking condition. Changing the gear ratioto 0.99:1 would then represent a driving condition.

Slip ratio is defined in a number of ways by different standards, butone way to express it is

Slip Ratio %=[(Vehicle Speed−Wheel Speed)/Vehicle Speed]×100,

where all velocities are linear. If the CVT gear ratio is set to 1.1:1(input speed to output speed), then the gear, which is moving at thesame linear velocity as the carriage, is moving faster than the linearvelocity of the tire, which must therefore be experiencing slip in thecontact patch as it “brakes”. Since the vehicle velocity is:

v=ωRgear,

the slip ratio therefore becomes:

Slip Ratio %=[(1.1ωRgear−1.0ωRtire)/1.1ωRgear]×100, or 9%.

Note that the slip ratio is the controlled parameter rather than aparameter calculated from trying to control two independent velocities.Note too that the slip ratio will be independent of carriage velocity.

Using the carriage and gearing systems described above, an overall testcarriage 20 is presented in FIG. 8. The figure shows the drive system 90for the carriage, as well as the coupled variable gear ratio test tiredrive. A single motor 92 with dual output shafts is orientedhorizontally (although obviously there could be numerous perturbationsfor this design). A drivetrain 94 takes the output from the motor drive92 on the right hand side to a set of tires, gear, or other tractivedevice 96 that is used to propel the carriage down the track. The outputon the left side in the figure is attached to a transmission (planetarygear set or CVT) 98 which is then attached to a gear train or chain andsprocket set 100 to provide torque to the telescoping driveshaft 102 andtest tire 18. The CVT 98 controls the slip ratio through the gear ratiovalue. Any slip in the drive system 90 propelling the carriage 20 can bemeasured using an external metrology reference (for example, measuringthe velocity of the carriage 20 directly rather than the rotationalspeed of the tires).

FIG. 17 illustrates the concept for a high-speed cable drive system 110.In this system 110, the cable 112 remains relatively stationary withregards to the track, rail, or ground 114. The purpose is to avoidissues with moving the cable 112 at high speeds around a pulley systemand risking it jumping the supporting pulley structure. A motorizedrotating drum 116 is mounted on the carriage 20, and the cable 112 isrotated around the drum 116 and tensioned with an idler pulley. As thedrum 116 begins to rotate, friction between the cable 112 and the drum116 minimizes slip, and the carriage 20 is pulled along the track. Inthis case, sections of the cable 112 remain stationary until thecarriage 20 approaches that particular section. Once the carriage 20arrives at that section, that section of the cable 112 will rapidlycirculate around the drum 116 but will then return to rest against therail 114. The cable 112 can either be fixed on two extremes of a lineartrack or, in the case of an oval or circular track, tensioned such thatsignificant friction between the cable 112 and the track prevent thecable 112 from slipping relative to the track. The illustratedconfiguration also shows the ability to couple a separate carriage 120to the driven carriage 20.

In one exemplary embodiment, the present invention further provides amethodology to accurately control slip ratio for tire testing machines.Tire testing machines are routinely used to measure the forces andmoments generated by a tire in operation. Typical tire testingtechniques include one of two methods: 1) mount the test tire on amovable spindle located beneath or behind a vehicle or a trailer, or 2)use a fixed lab system where the tire is run on a drum or a belt surfaceto replicate the tire/road surface.

Much of tire testing is conducted under a free rolling state, where notorque is applied to the test tire. However, tire forces and moments areextremely important under both driving and braking conditions. Thetrailer and vehicle-based systems typically do not have much capacityfor braking and none for driving due to the mechanisms, power, andcomplexity required. Only a few belt machines attempt to provide drivingor braking torque. However, such torque data is vitally important toauto manufacturers, race teams, and anyone doing simulations, and it isalmost exclusively based on the independent variable, slip ratio.

Slip ratio is defined in a number of different ways, but, in general,represents the ratio of the linear velocity of the tire in the contactpatch with the actual linear velocity of the vehicle (or the linearvelocity of the belt).

Currently, belt systems struggle to maintain a constant or controlledslip ratio. There are many reasons for this. First, these belt systemsconsist of two independent drive/brake systems with their owncontrollers designed to maintain constant torque on either the test tireor the belt. One drive motor (usually hydraulic or electric) is locatedon the spindle and provides driving torque to the test tire, or abraking system is used to provide the braking torque. A separate drivemotor/controller system is used to maintain the velocity of the beltsystem.

The challenge with this configuration is in maintaining a consistentslip ratio. Since the tire/belt interface contains a highly variable,stick-slip dynamic, it becomes difficult to maintain a constant velocityin either the test tire or the belt (or drum). This results in a very“noisy” calculation of slip ratio, with reported results jumping fromslip ratios of 11% to 7% in a single data point.

The approach of the present invention is, in essence, to providedisplacement inputs, rather than torque inputs. This is illustrated inFIG. 18. In this configuration, the drum, belt, or vehicle 200 iscoupled with the test tire 202 with mechanical gearing 204. In thisscenario, the velocity of the test tire 202 is mechanically linked,through some predetermined gear ratio, with the velocity of the drum,belt, or vehicle 200. The mechanical link 204 ensures that the slipratio is carefully controlled and consistent, although the torques onthe test tire 202 and drum, belt, or vehicle 204 may be highly dynamic.If the gearing mechanism 204 is such that it can be changed dynamicallythrough computer control or other, then the slip ratio can be carefullycontrolled and dynamically changed during a test, providing the abilityto “dial in” the required slip ratio with high resolution, as has notbeen previously possible.

This dynamic slip ratio control would provide the first capability toprovide smooth, clean tire data based on the slip ratio independentvariable. This improvement would significantly improve the ability tosimulate the performance of a vehicle, since most simulations pull databased on the input slip ratio.

This slip ratio control can be realized through a variety of differentgear mechanisms and arrangements 204. For example, the variable gearratio could be achieved through the implementation of a continuouslyvariable transmission, or CVT. A second arrangement could include thatillustrated in FIG. 19, wherein the drum, belt, drive wheel, or roadsurface 200 is coupled to the test tire 202 via a worm gear 206, a ringgear 208, and a plurality of bevel gears 210, as illustrated.

The above concept involves:

-   -   1) The use of a mechanical drive to control the ratio of speeds        between the test tire and the “road surface” (that could be an        actual road through the velocity of the vehicle, or a simulated        road such as a drum or belt, or other).    -   2) The use of a mechanical, electrical, or other mechanism that        provides a mechanical advantage to better control these ratios,        i.e. replacing the use of torque motors with a mechanically        linked ratio of speeds.    -   3) The mechanism allows dynamic modification of the gear ratio,        and therefore the slip ratio. This dynamic modification can be        through computer control, some form of actuation, or other        means. Any mechanism that allows the modification of gear ratio        without stopping or slowing the test tire is contemplated        herein.    -   4) The mechanism allows an “infinitely variable” gear ratio,        rather than a set number of gear ratios (such as a collection of        sprockets, such as on a bike).

In general, railed tire testing facilities have previously beenillustrated and described that utilize a pipe or “T” shaped rail. Thepresent invention also contemplates a refined rail for use in suchrailed tire testing facilities. This allows for the associated carriageto be minimally, but sufficiently, constrained. Referring specificallyto FIG. 20, the “T” shaped rail 300 significantly aids with precisionbecause one can control the thickness of the plates reasonably well. Theproblem is that fabricating the “T” is difficult and expensive. It isshown bolted here, but is more affordable when welded, and that has itsown difficulties, including still be expensive and having severe warpingproblems.

Referring to FIGS. 21-24, what is suggested is that the flat plates ofthe “T” are separated into substantially horizontal plates 302 andsubstantially vertical plates 304, each independent of one another, suchthat full adjustability of both horizontal and vertical rails isprovided, and saving on welding, etc. As illustrated, the lateralpositioning of the rail can be easily adjusted using the anchors to“dial in” and straighten the track. The same is true for the horizontaltracks. This design would be suitable for any railed mechanism whereprecision is important.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention, are contemplatedthereby, and are intended to be covered by the following claims.

What is claimed is:
 1. A tire testing system, comprising: one of asimulated road surface and an actual road surface; a test tirephysically contacting the one of the simulated road surface and theactual road surface; and a mechanical linkage linking the test tire andthe one of the simulated road surface and the actual road surface, suchthat the velocities of the test tire and the one of the simulated roadsurface and the actual road surface are linked and an associated slipratio between the test tire and the one of the simulated road surfaceand the actual road surface is controlled.
 2. The tire testing system ofclaim 1, wherein the simulated road surface comprises one of a drum, abelt, a drive wheel, and a rail.
 3. The tire testing system of claim 1,wherein the mechanical linkage is varied in terms of gear ratio using acontroller such that slip ratio is dynamically controlled and varied. 4.The tire testing system of claim 1, wherein the mechanical linkagecomprises one of a plurality of gears that provide control of gear ratioand a continuously variable transmission.
 5. The tire testing system ofclaim 1, wherein the mechanical linkage comprises a worm gear, a ringgear, and a plurality of bevel gears.
 6. The tire testing system ofclaim 1, wherein the mechanical linkage also selectively provides thetest tire with a free-rolling state.
 7. A tire testing method,comprising: providing one of a simulated road surface and an actual roadsurface; providing a test tire physically contacting the one of thesimulated road surface and the actual road surface; and providing amechanical linkage linking the test tire and the one of the simulatedroad surface and the actual road surface, such that the velocities ofthe test tire and the one of the simulated road surface and the actualroad surface are linked and an associated slip ratio between the testtire and the one of the simulated road surface and the actual roadsurface is controlled.
 8. The tire testing method of claim 7, whereinthe simulated road surface comprises one of a drum, a belt, a drivewheel, and a rail.
 9. The tire testing method of claim 7, wherein themechanical linkage is varied in terms of gear ratio using a controllersuch that slip ratio is dynamically controlled and varied.
 10. The tiretesting method of claim 7, wherein the mechanical linkage comprises oneof a plurality of gears that provide control of gear ratio and acontinuously variable transmission.
 11. The tire testing method of claim7, wherein the mechanical linkage comprises a worm gear, a ring gear,and a plurality of bevel gears.
 12. The tire testing method of claim 7,wherein the mechanical linkage also selectively provides the test tirewith a free-rolling state.
 13. A tire testing system, comprising: afirst rail and a second rail, wherein one or more of the first rail andthe second rail comprise separate substantially horizontal andsubstantially vertical plates; a carriage assembly coupled to the firstrail and the second rail such that five degrees of freedom of motion ofthe carriage assembly are thereby constrained; a first bogie assemblycoupling the carriage assembly to the first rail such that at leastlateral, pitch, and yaw motions of the carriage assembly are therebyconstrained; and a second bogie assembly coupling the carriage assemblyto the second rail such that at least vertical and roll motions of thecarriage assembly are thereby constrained; wherein the carriage assemblytranslates in a direction that is tangential to the first rail.